Body mass index is weight divided by height squared - a rough screening number, not a diagnosis. Enter your height and weight in either metric or imperial units to see your BMI, the category it falls in, and what weight range would put you in the 18.5 to 25 band.
Below 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight and 30 or above is obese. These thresholds are for adults; children are assessed against age and sex percentiles instead.
As a population screening tool it is useful. For an individual it can mislead badly, because it cannot distinguish muscle from fat or account for frame size and fat distribution. Muscular athletes routinely score as overweight. Waist circumference and body fat percentage add information BMI misses.
No. Health risk starts to rise at a lower BMI in some South and East Asian populations, and several health bodies use a lower overweight threshold of 23 for those groups. BMI is a starting point for a conversation with a clinician, not a verdict.